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Critical New Flaw Found in IIS 5.0

A critical, newly discovered flaw in Internet Information Services 5.0 could open Windows 2000-based Web servers, and other Windows 2000 systems that were installed with default settings, to a code execution vulnerability.

Microsoft issued a security bulletin about the problem early Tuesday morning. The problem is severe enough that Microsoft pushed the announcement up nearly two days from its usual patch release time, which is Wednesday night.

The problem arises from an unchecked buffer in a component of Microsoft's implementation of the World Wide Web Distributed Authoring and Versioning (WebDAV) protocol, a set of extensions to HTTP for editing and file management between computers on the Internet.

"An attacker could exploit the vulnerability by sending a specially formed HTTP request to a machine running Internet Information Server," Microsoft's security bulletin stated. "The request could cause the server to fail or to execute code of the attacker's choice. The code would run in the security context of the IIS service (which, by default, runs in the LocalSystem context)."

Officials with the SANS Institute suggested the flaw was a prime candidate for a Code Red style attack. They encouraged administrators to clamp down the hole "before the race to complete the 'WebDAV Worm' is completed."